Hydrogeological instability is one of the most serious problems facing Italy, so much so that Europe has allocated about 2.5 billion euros to Italy through the PNRR (National Recovery and Resilience Plan), to be spent by 2026. The government has not so far decided how to invest these funds, but what is certain is that they must be used by the Ministry for the Environment and Local Authorities – through projects presented by the individual regions – to develop engineering containment works such as retention basins, detention basins, river drainage and so on. But what is hydrogeological instability, what causes it and what possible practical solutions are there?
Hydrogeological instability: the meaning
The Italian Encyclopedia Treccani defines hydrogeological instability as an “environmental degradation chiefly due to erosion by surface waters, in geological situations that are naturally subject to this phenomenon (argillaceous or arenaceous rock, or other types of rock with weak cementation), or land that has been by stripped bare by intensive deforestation. So it is a phenomenon that affects the land, and hence everything that stands on the land, such as structures, buildings and towns and cities. Now that we know what hydrogeological instability is, we can go on to identify the causes of this phenomenon.
The causes of hydrogeological instability
There are many possible causes of hydrogeological instability. The phenomenon tends to occur most frequently in areas that are naturally exposed to it as a result of their morphology. For example, mountainous or hilly areas that have reservoirs, especially the smaller reservoirs. These expanses of water are more exposed to the risk of overflow in the event of heavy rain, giving rise to further phenomena such as water erosion, and hence landslides and floods. However, we should not overlook the causes of hydrogeological instability that result from human activity: this includes deforestation, uncontrolled urban development, illegal construction, the creation of quarries, the abandonment of previously cultivated land on high ground, unsustainable agricultural practices, invasive interventions on water courses, hydrocarbon extraction and so on. We also need to take into account climate change, which may have a significant effect on hydrogeological instability as a result of increasingly frequent heavy rain or cloudbursts. So hydrogeological instability may be caused by a number of factors linked to morphology and human activity.
Hydrogeological instability in Italy
As we saw earlier, hydrogeological instability is an important issue for Italy today. According to data from the Italian Institute for Environmental Protection and Research (ISPRA), which is responsible for monitoring the state of the land across Italy and analysing the consequences of events caused by hydrogeological instability, Italy is one of the European countries most exposed to this risk. As stated in a recent ISPRA report on the topic, Italy has over 565,000 buildings that are exposed to the risk, as well as almost 12,000 assets of cultural interest. And that’s not all: that number would be higher if you take into account all the buildings that are exposed “simply” to flood risk. The ISPRA statistics also reveal that about two thirds of the landslips recorded in Europe occurred in Italy. A classification table of areas exposed to the danger of hydrogeological instability has been produced, showing that 12,405 square kilometres of land are at high risk, while 25,398 square kilometres are classified as medium risk.
These figures confirm the fragility of Italian territory in this respect, helping to explain some of the disastrous events that have occurred in Italy in recent decades.
Legislation has been passed from the late 1980s onwards in order to limit and contain the problem of hydrogeological instability in Italy as far as possible. Firstly, there was the Framework Law no.183 of 18 May 1989, aimed at creating a plan for hydrogeological basins.
More recently, Law 109/2018 required the creation of a Strategy for Italy, a type of control room with the task, among others, of verifying the actual implementation of works to reduce risks for Italian territory, including the phenomenon of hydrogeological instability. On 20 February the following year (2019), the National Plan for Mitigation of Hydrogeological Risk was approved, which sets out specific programmes and objectives; two years later, in 2021, the roles of Government Commissioners for combating hydrogeological instability were created.
As we mentioned at the beginning, Italy also has funds available from the PNRR to be used for monitoring and reducing hydrogeological risk. Apart from the use to be made of these funds, according to the ReNDiS report by ISPRA, the Ministry for the Environment has allocated almost 7 billion euros over 20 years to finance over 6,000 projects; however, we should point out that about 36 billion euros would be required to finance all the projects that have been proposed.
Solutions to the problem of hydrogeological instability
What possible remedies are there for reducing hydrogeological instability? There are various solutions that could effectively be implemented, involving three areas of action: activities of prevention, anticipation, and mitigation of the effects. So we need to start with careful monitoring of the conditions of the territory, and move on to carry out studies that can identify the degree of danger and risk on a case by case basis. But we also need to make people aware of the problem, and, of course, carry out regular maintenance.
In many cases, the problem consists of the construction of buildings in areas exposed to risk, generally but not always illegally. So one of the main ways to combat hydrogeological instability is not to build in unsuitable areas, as well as implementing good building practice, starting with full knowledge of the terrain and its characteristics.
As we have said, urban development increases the risk of instability, and, where excessive, it can lead to a dangerous reduction in the drainage ability of the ground in the event of meteoric water. So green areas are important in this respect, along with the use of surface drainage systems and permeable road and pavement surfaces.
We have mentioned control of urban development and illegal construction, as well as creating green areas and surface draining systems. Other solutions include the regular maintenance and cleaning of water courses, reforestation, the regeneration of agricultural land on high ground and finally the regeneration and consolidation of land characterized as high risk.